[SI-LIST] Re: LC filters on power pins

sshhhhshh... trade secret that keeps us employed.


At 12:13 PM 09/27/2001 , David Kaiser wrote:

>I have a question about LC filters on power SERDES and other Gbit devices.
>
>Most SERDES venders provide app notes that suggests using LC filters on the
>power pins of these Gbit devices to prevent noise from getting on to the
>power planes. But it seems to me that the LC filter components would have no
>effect at these Gbit frequencies, and could in fact make matter worse
>because the power pins would have no more than maybe a small island of
>interplane capacitance for decoupling. It seems that it would be better to
>just tie the power pins directly to buired capacitance planes. What do the
>SI gurus think?
>
>Also, it seems that at multiple GHz frequencies, the return path for the
>noise on the power planes would be so short, that noise would be squelched
>to quickly to cause problems on the planes.
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----------------------------
Bill Owsley,   owsley@xxxxxxxxx
919) 392-8341

Compliance Engineer
Cisco Systems
7025 Kit Creek Road
POB 14987
RTP. NC. 27709


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